Lightweight Concrete for High Strength - Expanded Shale & Clay

s: slump (in)
γ ψ
⎧ 0.30 −1.4
⋅ψ
for ψ ≤ 0.50
= ⎨
; fine aggregate content factor
⎩0.90
− 0.2 ⋅ψ
for ψ > 0.50
ψ: fine aggregate-to-total aggregate ratio in decimals
γ = 0.75 + 0. 00036 ⋅ c ; cement content factor
c
c: cement content (lb/yd 3 )
γ α
= 0 .95 + 0. 08⋅α
; air content factor
α: air content (%)
µε.
After applying the factors above, ultimate shrinkage value is usually between 415 and 1070
B.3.2. AASHTO-LRFD Method (Normal Strength Concrete)
AASHTO-LRFD method (1998) is very similar to ACI-209 method, but it incorporates more
recent data. AASHTO-LRFD method proposes slightly different correction factors.
Creep Model. The general equation for creep coefficient is the same as ACI-209 (Equation B.1).
However the expression for calculating ultimate creep coefficient differs from ACI expression
(Equation B.2). Equation B.5 presents AASHTO-LRFD expression for ultimate creep
coefficient.
φ = 3. 50 ⋅ k ⋅ k ⋅ k ⋅ k
(B.5)
u
la
where
ø u : ultimate creep coefficient
k la
118
h
c
f
−0.
= 1.00 ⋅ t'
for moist curing ; age of loading factor
until ⎧ ⎡
⎤⎫
loading
⎪ ⎢ 4000
⎥⎪
t'
= ∑ ∆ti
⋅ exp⎨−
⎢
−13.
65⎥⎬
; maturity of concrete at loading (days)
⎪
T ( ∆t
)
⎢273
+
i
⎥⎪
⎩ ⎣
T 0 ⎦⎭
∆t i : period of time (days) at temperature T(∆t i ) ( o o
o
C) ( C = 0.556×
F −17.
778)
T 0 : 1 o C
k h
= 1 .58 − 0. 83⋅
h ; ambient relative humidity factor
B-7